Experienced tank here, who only picked it up in late vanilla/BC as an alt.
You CAN 'learn' to tank without going into dungeons, especially with a friend, mobs are the same anywhere, theyjust might nto live long enough elsewhere. I remember paladins being a bit of a pain early on because I don't think you get Consecrate until 20 something, which is pretty key to AE threat. Basically, your standard operating procedure is going to be:
1) Assess a pull. Just use your best judgement about mob placements to deduce how much stuff is going to come on a pull, and look at the names to try and figure out what is going to be the most critical to kill first. Typically healer-y sounding names are healers and need to die first, then dps casters, then melee mobs. Not always true, but it's a good rule of thumb for new pulls. Mark a skull on something you want people to focus down. This is universal and if someone pulls aggro on a non-skull its their own fault.
2) pull the mobs! This should be obvious, but I'm guessing you're stuck with avenger's shield and judgement at this point. Judging is probably the right way to pull (I tend to open with taunt later on, but since you lack any real AoE it's probably best to save it), rather than charging in USUALLY pulling back onto you is safer, so you won't aggro extra stuff. Try to use your shield once you're sure it'll hit the most mobs possible, if there are more mobs than the shield can hit, try to slap the others with your other abilities.
3) holding aggro! At this point once everything is on you, your job is simply to keep it on you. You need to be swapping targets fairly frequently, threat plates or a threat meter (omen) will do wonders for you here, you can swap to targets that you're closer to losing aggro on faster, but the real key is to ALWAYS be doing something, don't lose your focus on what abilities to use just because you're focusing on target swapping. Becoming very comfortable with your abilities is important for this. Once you're set on that you can easily play without even paying attention to your hotkeys or anything like that. Try to put MORE threat into the mob people are attacking (the skull). By the time that dies it should be a decent lead on everything else and you can either just follow what the dps is on (by looking at what they're gaining threat on) or mark something else (Conversely, you can mark more mobs pre-pull, X is typically second).
That's pretty much it at low levels. Just make sure righteous fury is always on, and be ready to hit any defensive cooldowns you need to if things get hairy. As a tank you set the pace of the dungeon, so people will look to you and get impatient with you, just stick it out and say you're new. Not everyone is a jerk. I personally pace a dungeon by watching my healer. Between packs target your healer and eyeball their mana, if they're burning 75% of their mana on every group, let them get up to like 80% or so before you pull the next one, fi they seem to be ok on mana, just keep pulling and get used to how much they're using up. Bosses will need a bit more and you usually want to let them fill up beforehand.
A quick glance at wowhead is telling me you'll need to be ~ level 20 before you get hammer of the righteous and a few more levels to get the talents to make consecrate beefy. This is basically just shitty design on Blizz' part in the redoing of the classes with cataclysm, it's going to be HARD to tank on your paladin until you have those abilities, they're your AE bread and butter, but y'know what? It's possible, and if you put in the work you can do it

We ALL had to tank like that back in the day - LOTS of active target swapping and frantic button mashing. If someone pulls aggro now and then it's not a huge deal in levelling dungeons.